Various methods have been proposed to improve ball control on tennis rackets. Generally, the object of the methods is to increase the effective hitting area of the head (sweet spot or center of percussion). Thus, U.S. Pat. No. 3,999,756 discloses a tennis racket, the construction of which is adapted to increase the string area, thus giving a high restitution coefficient.
Another method having the same kind of object is disclosed in U.S. Pat. No. 3,801,099 (Lair) which concerns a tennis racket with a low weight to stiffness ratio and the head frame of which is shaped in order that the longer axis of the head ellipse is perpendicular to the handle axis; this arrangement increases the moment of inertia around the racket handle axis.
U.S. Pat. No. 3,907,292 concerns a tennis racket the rim and the handle of which are surrounded by a tubular organ containing a series of fly-weights which normally rest in the throat portions of the tube due to the action of helical springs. Under use, the weights move toward the head of the racket because of the centrifugal force resulting from the racket swinging motion during play and increase the "sweet spot" of the stringed area; this also ensures a better bouncing control on the ball and an increased hitting power.
U.S. Pat. No. 3,941,380 (Lacoste) discloses a tennis racket in which the head oscillations are damped by means of a secondary oscillator working along the handle axis thereof at vibration antinodes. Since the oscillating bodies are located on the longitudinal axis of the racket, they do not affect the center of percussion and do not reduce the torque around the axis which results from an off-centered impact.
U.S. Pat. No. 4,057,250 (Kuban) discloses means to generate a reactive force for diminishing the bouncing of the racket after ball impact. For achieving this, masses producing the force must be able to move as freely as possible and, in this connection, the masses can even consist of loose metal shot. Thus, the device is not a secondary oscillator. The effect is distinguishable from the present invention since the increase of the moment of inertia of the racket in Kuban will only take place when the body has reached the end of its free elastic displacement which may be too late after the impact for being effective to increase the center of percussion. Moreover no damping of vibration is contemplated by an oscillator.
Another reference, French Pat. No. 2,387,670, concerns a golf club, the head of which is provided with balancing weights which can vibrate in a direction perpendicular to the longitudinal axis of said head. This oscillating motion ensures that the orientation of the head is maintained during the interval starting from the moment the ball is hit by the head to the moment it loses contact therewith after being hit. The balancing weights increase the moment of inertia of the club in relationship to the hitting point of the head. Thus, these weights have first a static effect because they increase the club inertia and, second, they have a dynamic effect because they move in a direction perpendicular to the hitting plane of the head. Such displacements generate moments of inertia around the striking point which are substantially equal and enable the head to stay properly oriented after striking the ball, this action being effective for the full distance where the head and the ball stay in contact.